Messages in this thread | | | Date | Wed, 3 Aug 2022 10:42:06 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] sched/debug: avoid executing show_state and causing rcu stall warning |
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On Wed, Aug 03, 2022 at 07:14:52PM +0200, Ingo Molnar wrote: > > * Paul E. McKenney <paulmck@kernel.org> wrote: > > > There is an rcu_sysrq_start() and rcu_sysrq_end() to suppress this. > > These are invoked by __handle_sysrq(). The value of > > rcu_cpu_stall_suppress should be non-zero during the sysrq execution, and > > this should prevent RCU CPU stall warnings from being printed. > > > > That said, the code currently does not support overlapping calls to the > > various functions that suppress RCU CPU stall warnings. Except that the > > only other use in current mainline is rcu_panic(), which never > > unsuppresses. > > > > So could you please check the value of rcu_cpu_stall_suppress? Just in > > case some other form of suppression was added somewhere that I missed? > > So instead of supressing the (justified!) RCU stall messages, I'd much > rather we apply only the minimal locking necessary for this debug printout. > > That should also solve the stall warnings as a side effect.
I am certainly with you in spirit! If I recall correctly, the issue that led to the current state was that there was no way to walk the task list locklessly except under an RCU read-side critical section. Yes, you can use get_task_struct(), but that only prevents that task structure from being freed, not from being removed from the list.
Here is hoping that there is a better way to nail down a task while RCU-pausing a task-list traversal. Thoughts?
Thanx, Paul
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